Commit message: Don't do any work when reshaping 0 elements sparse tensor.

If reshaping to 0 elements tensor, check that input has no elements.
If reshaping no elements input, check that output has no elements.

PiperOrigin-RevId: 388296986
Change-Id: Iadc9fe7252e14313ca987e69bf0d7042fd10232a
CVE: CVE-2021-37640
CWE: CWE-369
Vulnerability description: TensorFlow is an end-to-end open source platform for machine learning. In affected versions the implementation of `tf.raw_ops.SparseReshape` can be made to trigger an integral division by 0 exception. The [implementation](https://github.com/tensorflow/tensorflow/blob/8d72537c6abf5a44103b57b9c2e22c14f5f49698/tensorflow/core/kernels/reshape_util.cc#L176-L181) calls the reshaping functor whenever there is at least an index in the input but does not check that shape of the input or the target shape have both a non-zero number of elements. The [reshape functor](https://github.com/tensorflow/tensorflow/blob/8d72537c6abf5a44103b57b9c2e22c14f5f49698/tensorflow/core/kernels/reshape_util.cc#L40-L78) blindly divides by the dimensions of the target shape. Hence, if this is not checked, code will result in a division by 0. We have patched the issue in GitHub commit 4923de56ec94fff7770df259ab7f2288a74feb41. The fix will be included in TensorFlow 2.6.0. We will also cherrypick this commit on TensorFlow 2.5.1 as this is the other affected version.

Project: tensorflow
File: reshape_util.cc

void ReshapeSparseTensor(OpKernelContext *context,
                         const Tensor &input_indices_in,
                         const Tensor &input_shape_in,
                         const Tensor &target_shape_in, int output_indices_idx,
                         int output_shape_idx) {
  OP_REQUIRES(context, TensorShapeUtils::IsMatrix(input_indices_in.shape()),
              errors::InvalidArgument(
                  "Input indices should be a matrix but received shape ",
                  input_indices_in.shape().DebugString()));
  OP_REQUIRES(context, TensorShapeUtils::IsVector(input_shape_in.shape()),
              errors::InvalidArgument(
                  "Input shape should be a vector but received shape ",
                  input_shape_in.shape().DebugString()));
  OP_REQUIRES(context, TensorShapeUtils::IsVector(target_shape_in.shape()),
              errors::InvalidArgument(
                  "Target shape should be a vector but received shape ",
                  target_shape_in.shape().DebugString()));

  const int64_t output_rank = target_shape_in.NumElements();
  const TensorShape input_shape(input_shape_in.vec<int64>());
  const int64_t dense_size = input_shape.num_elements();
  const int64_t nnz = input_indices_in.shape().dim_size(0);

  // Compute the output shape. Determine product of specified dimensions, and
  // find the index of the unspecified one.
  TensorShape output_shape;
  int64_t product = 1;
  int unknown_index = -1;
  auto target_shape = target_shape_in.vec<int64>();
  for (int d = 0; d < output_rank; ++d) {
    const int64_t size = target_shape(d);
    if (size == -1) {
      OP_REQUIRES(
          context, unknown_index == -1,
          errors::InvalidArgument("only one output dimension may be -1, "
                                  "not both ",
                                  unknown_index, " and ", d));
      unknown_index = d;
      output_shape.AddDim(1);
    } else {
      OP_REQUIRES(context, size >= 0,
                  errors::InvalidArgument("size ", d,
                                          " must be non-negative, not ", size));
      product *= size;
      output_shape.AddDim(size);
    }
  }
  if (unknown_index != -1) {
    OP_REQUIRES(
        context, product > 0,
        errors::InvalidArgument("reshape cannot infer the missing "
                                "input size for an empty tensor unless all "
                                "specified input sizes are non-zero"));
    const int64_t missing = dense_size / product;
    OP_REQUIRES(
        context, product * missing == dense_size,
        errors::InvalidArgument(
            "Input to reshape is a SparseTensor with ", dense_size,
            " dense values, but the requested shape requires a multiple of ",
            product, ". input_shape=", input_shape.DebugString(),
            " output_shape=", output_shape.DebugString()));
    output_shape.set_dim(unknown_index, missing);
  }

  OP_REQUIRES(
      context, output_shape.num_elements() == dense_size,
      errors::InvalidArgument("Input to reshape is a tensor with ", dense_size,
                              " dense values, but the requested shape has ",
                              output_shape.num_elements(),
                              ". input_shape=", input_shape.DebugString(),
                              " output_shape=", output_shape.DebugString()));

  // Optimize for reshaping to the same shape.
  if (input_shape == output_shape) {
    context->set_output(output_indices_idx, input_indices_in);
    context->set_output(output_shape_idx, input_shape_in);
    return;
  }

  Tensor *result_shape = nullptr;
  OP_REQUIRES_OK(context, context->allocate_output(output_shape_idx,
                                                   TensorShape({output_rank}),
                                                   &result_shape));
  auto output_shape_vec = result_shape->vec<int64>();
  for (int j = 0; j < output_shape.dims(); ++j) {
    output_shape_vec(j) = output_shape.dim_size(j);
  }

  Tensor *result_indices = nullptr;
  OP_REQUIRES_OK(context,
                 context->allocate_output(output_indices_idx,
                                          TensorShape({nnz, output_rank}),
                                          &result_indices));
  if (nnz > 0) {
    OP_REQUIRES_OK(context, functor::ReshapeSparseTensorFunctor<Device>()(
                                context, input_shape, output_shape,
                                input_indices_in.matrix<int64>(),
                                result_indices->matrix<int64>()));
  }
}